Phase meter for comparing rectangular waves

ABSTRACT

A large-band phase meter operating by the evaluation of displaced rectangular waves being applied to phase measurements, particularly between two waves having the same frequency but different cyclic ratios furnishing measurements independent of the cyclic ratio.

United States Patent Salle et al.

PHASE METER FOR COIVIPARING RECTANGULAR WAVES Inventors: Yves Salle,Boulonge; Marcel Pincemin, Ris Orangis, both of France Assignee:Compagnie Industrial Des Telecommunications, Cit-Alcatel, Paris, FranceFiled: Feb. 25, 1972 Appl. No.: 229,338

US. Cl. ..324/83 A, 328/109 Int. Cl. ..G01r 25/00 Field of Search..324/83 R, 83 A, 83 D;

[451 Apr. 17, 1973 [56] References Cited UNITED STATES PATENTS 3,482,13212/1969 Emde ..307/21O 3,551,808 12/1970 Grossimon et a1. ..324/83 D XPrimary ExaminerA1fred E. Smith Attorney-Paul M. Craig, Jr. et a1.

[ 5 7 ABSTRACT A large-band phase meter operating by the evaluation ofdisplaced rectangular waves being applied to phase measurements,particularly between two waves having the same frequency but differentcyclic ratios furnishing measurements independent of the cyclic ratio 7Claims, 6 Drawing Figures vIIIw e A'A'A A'A'A 3 65 e2 60 nAAAlA IPATENTEDAPR 1 71915 SHEET 2 BF 3 FIG.3

FIG.4

PHASE METER FOR COMPARING RECTANGULAR WAVES The present inventionrelates in general to the field of large-band phase meters.

It is directed more particularly to a phase meter which operates byevaluation of shifted rectangular pulse waveforms and has application tophase measurements, particularly between two waves having the samefrequency but different cyclic ratios.

It is known in the art to construct phase meters which operate by meansof an evaluation of the angular separation between the zero crossing ofthe rising fronts of two waves, for example, two waves having the samefrequency and being offset in phase with respect to each other. Inpractice the measurement is carried -out on rectangular pulse waveformswhich are obtained by amplification and amplitude limiting of the twowaves to be phase metered. This method produces correct results, if,from two sinusoidal waves, one obtains two rectangular waves with cyclicratios of 1/1, or at least ratios which are equal with respect to eachother. But this is an ideal case which is rarely obtained in practice.

In actual fact, the waves which arrive at the phase meter in theconventional case have hypothetically followed different paths, and haveundergone various manipulations susceptible to more or less alteringtheir characteristics, which is the reason why, in a large number ofcases, the rectangular waves which the phase meter receives do not havecyclic ratios of 1/1 or ratios which are equal to each other.

In order to obtain a correct measurement of the phase shift in spite ofthese frequency encountered unfavorable conditions, the presentinvention has recourse to simple logic means actuated by the forward andbackward fronts of the rectangular waves to be compared to provide anaccurate phase measurement.

The principle of the present invention will now be further explained indetail with reference to the accompanying drawings, wherein:

FIG. 1 comprises three waveforms which show the result of the phasedifference measured for two waves having a cyclic ratio of l/ 1 in afirst case of phase shifting;

FIG. 2 comprises three waveforms which show the result of the phasedifference measured for two waves having a cyclic ratio of 1/ I in asecond case of phase shifting;

FIGS. 3 and 4 each comprise three waveforms which are similar to thoseof FIGS. 1 and 2 but correspond to cases involving waves havingdifferent cyclic ratios;

FIG. 5 is a schematic diagram of an apparatus according to the presentinvention applying the theory expressed in FIGS. 1 to 4, and

FIG. 6 is a schematic circuit diagram of one detail of the diagram ofFIG. 5, and illustrating three waveforms which aid in explaining theoperation of the circuit of FIG. 6.

FIG. 1 illustrates two rectangular waves A and B having a cyclic ratioof III and on which the rising and descending fronts have been indicatedby arrows. The duration of the period of these waves has been designatedwith reference symbol T. The period t] is the interval which separates arising front of waveform A from the following descending front ofwaveform B,

or the descending front of waveform A from the following rising front ofwaveform B. Therefore, waveform A leads waveform B by the time intervalT/2 :1.

It is assumed that under these conditions an appropriate circuit, whichwill be further described hereinbelow, generates a wave e1 formed ofnegative pulses designated alternately a and b and having a uniformlevel with a width t1. The direct-current component of this signal e1 isnegative and proportional to t1 el k.tl.

In FIG. 2 the two waves A and B are offset in phase but to a differentextent from the example of FIG. 1. The period t2 is the interval whichseparates a rising front of waveform B from the following descendingfront of waveform A, or a descenting front of waveform B from thefollowing rising front of waveform A. Thus, waveform A leads waveform Bby the time interval T/2 :2.

It is assumed that under these conditions the same circuit as referredto hereinabove generates a wave e2 formed of positive pulses designatedalternately c and d and having a uniform level, with a width t2. Thedirectcurrent component of this signal e2 is positive and proportionalto t2 e2 k.t2.

The direct-current component of the signal e (either e1 or 22) is thusnull with respect to the phase opposition between waveforms A and B andpasses from a positive value, for example +E, for a zero phase shift toa negative value E for a phase shift of 360, with the law of variationbetween the two being linear.

In the waveform diagram of FIG. 3 it is assumed that the cyclic ratiosof the waveforms A and B are different; and specifically, that the ratioof B is greater than that of A. The measuring circuit then furnishes awave e3 formed of positive pulses c alternating with negative pulses bhaving an equal width. The directcurrent component of this signal iszero.

In the example of FIG. 4 it is assumed that the cyclic ratio of waveformA is greater than that of waveform B. The measuring circuit thenfurnishes a wave e4 formed of negative pulses a alternating withpositive pulses d having an equal width. The direct-current component ofthis signal is zero.

Now, in the case of different cyclic ratios, as in the case of cyclicratios equal to 1/1, the measuring circuit furnishes a zero outputcurrent for the phase opposition. One could show without difficulty thatthe law of variation from Oto 360is the same as in the case of equalcyclic ratios.

FIG. 5 illustrates one example of a circuit furnishing signals accordingto FIGS. 1 and 3. The wave A is applied to an input terminal 1 and thewave B is applied to an input terminal 2. A signal e furnishing acurrent representing a linear function of the phase shift between thewaves A and B is extracted from an output terminal 3.

The circuit includes four monostable flip-flops 11 14 furnishing veryshort pulses (for example, smaller than 5 percent of the shortest periodof the waves A and B) having a descending front. The flip-flop 11receives the signal A directly from terminal 1 and the flip-flop 12receives the signal A through an inverter 15. The flip-flop 13 receivesthe signal B directly from terminal 2 and the flipflop 14 receives thesignal F through an inverter 16. For that reason, the flip-flop 11furnishes short pulses Al on the descending fronts of waveform A and theflip-flop l2 furnishes short pulses A2 on the rising fronts of waveformA. The flip-flop 13 furnishes short pulses B1 on the descending frontsof B and the flip-flop 14 furnishes short pulses B2 on the rising frontsof B.

A subassembly 20 comprises three AND circuits with two input gates 21and 22 and an output gate 23. Gate 21 receives the signal Al on oneinput and the signal on the other input which is connected to an inputof gate 22. The outputs of gates 21 and 22 are connected to the inputsof gate 23 whose output is connected back to the second input of gate22.

The subassemblies 30, 40, and 50 are mounted in the same fashion as thesubassembly 20 vis-a-vis the signals A2, B1 and B2, respectively. Thesignal T3; is applied to the common inputs of gates 21 and 22; thesignal B is applied to the common inputs of gates 31 and 32; the signalA is applied to the common inputs of gates 41 and 42; and the signal Ais applied to the common inputs of gates 51 and 52.

A conventional operational amplifier 60 having a negative input 61 and apositive input 62 is connected to the subassemblies 20 50. The input 61is connected to the output a of the subassembly 20 through a resistor 63and to the output b of the subassembly 30 through a resistor 64. Theinput 62 is connected to the output c of the subassembly 40 through aresistor 65 and to the output d of the subassembly 50 through a resistor66.

A negative feedback resistor 67 is connected between the output 3 andthe terminal 61 of the operational amplifier 60, and all of theresistors 63 through 67 are preferably equal.

The outputs a, b, c, and d of the subassemblies 20 50 correspond to thesignals which have been indicated in the drawing FIGS. 1 to 4 by thesame designations.

A subassembly, such as 20, is reproduced in FIG. 6. This circuit isknown in the art as a validation circuit. Receiving on the one hand asignal D, a so-called validation signal, and on the other hand a pulseA1 at the inside of the signal B, it furnishes at the output a signal bwhich lasts from the beginning of the pulse Al to the end of thevalidation pulse F The forms of the signals F, Al and b have beenillustrated in FIG. 6. It is understood that equivalent operations areperformed by the subassemblies 30, 40, and 50. It can therefore beeasily seen that the circuit of FIG. produces the signals described inFIGS. 1, 2, 3, and 4 for the corresponding conditions.

What is claimed is:

l. A phase meter for measuring the phase displacement between arectangular wave A and a rectangular wave B and providing a directcurrent voltage varying between a positive maximum value for a measuredphase displacement of 0 and a negative maximum value for a phasedisplacement of 360 in accordance with a linear law of variation,comprising four monostable flip-flops, means responsive to therectangular waves A and B for providing the respective signals A, A, Band to the input of a respective monostable flipflop, four validationcircuits each having one input connected to the output of acorresponding monostable flip-flop and another input receiving thesignals E, B, A and A, respectively, and an operational amplifier havinga ne ativ e input terminal connected to the outputs 0 two 0 saidvalidation circuits and a positive mput terminal connected to theoutputs of the other two validation circuits.

2. A phase meter as defined in claim 1 wherein said means responsive tothe rectangular waves includes a first input terminal connecting saidwave A directly to a first one of said monostable flip-flops, a firstinverter connecting said first input terminal to a second one of saidmonostable flip-flops, a second input terminal connecting said wave Bdirectly to a third one of said monostable flip-flops and a secondinverter connecting said second input terminal to the fourth one of saidmonostable flip-flops.

3. A phase meter as defined in claim 2 wherein each validation circuitincludes first, second, and third AND gates each having a pair ofinputs, the outputs of said first and second AND gates being connectedto the respective inputs of said third AND gate whose output isconnected to an input of said second AND gate, the other input of saidsecond AND gate and an input of said first AND gate being connectedtogether to form one input of said validation circuit and the otherinput of said first AND gate forming the other input of said validationcircuit.

4. A phase meter as defined in claim 3 wherein the output of eachvalidation circuit is connected to an input of said operationalamplifier through a respective resistor, all of the resistors connectedto the inputs of said operational amplifier having an equal value.

5. A phase meter as defined in claim 4 wherein said operationalamplifier includes a feedback resistor connected between its output andits negative input terminal, said feedback resistor having the samevalue as the resistors connected between said validation circuits andthe input terminals of said operational amplifier.

6. A phase meter as defined in claim 1 wherein each validation circuitincludes first, second, and third AND gates each having a pair ofinputs, the outputs of said first and second AND gates being connectedto the respective inputs of said third AND gate whose output isconnected to an input of said second AND gate, the other input of saidsecond AND gate and an input of said first AND gate being connectedtogether to form one input of said validation circuit and the otherinput of said first AND gate forming the other input of said validationcircuit.

7. A phase meter as defined in claim 1 wherein the output of eachvalidation circuit is connected to an input of said operationalamplifier through a respective resistor, all of the resistors connectedto the inputs of said operational amplifier having an equal value.

1. A phase meter for measuring the phase displacement between arectangular wave A and a rectangular wave B and providing a directcurrent voltage varying between a positive maximum value for a measuredphase displacement of 0* and a negative maximum value for a phasedisplacement of 360* in accordance with a linear law of variation,comprising four monostable flip-flops, means responsive to therectangular waves A and B for providing the respective signals A, A, Band B to the input of a respective monostable flip-flop, four validationcircuits each having one input connected to the output of acorresponding monostable flipflop and another input receiving thesignals B, B, A and A, respectively, and an operational amplifier havinga negative input terminal connected to the outputs of two of saidvalidation circuits and a positive input terminal connected to theoutputs of the other two validation circuits.
 2. A phase meter asdefined in claim 1 wherein said means responsive to the rectangularwaves includes a first input terminal connecting said wave A directly toa first one of said monostable flip-flops, a first inverter connectingsaid first input terminal to a second one of said monostable flip-flops,a second input terminal connecting said wave B directly to a third oneof said monostable flip-flops and a second inverter connecting saidsecond input terminal to the fourth one of said monostable flip-flops.3. A phase meter as defined in claim 2 wherein each validation circuitincludes first, second, and third AND gates each having a pair ofinputs, the outputs of said first and second AND gates being connectedto the respective inputs of said third AND gate whose output isconnected to an input of said second AND gate, the other input of saidsecond AND gate and an input of said firSt AND gate being connectedtogether to form one input of said validation circuit and the otherinput of said first AND gate forming the other input of said validationcircuit.
 4. A phase meter as defined in claim 3 wherein the output ofeach validation circuit is connected to an input of said operationalamplifier through a respective resistor, all of the resistors connectedto the inputs of said operational amplifier having an equal value.
 5. Aphase meter as defined in claim 4 wherein said operational amplifierincludes a feedback resistor connected between its output and itsnegative input terminal, said feedback resistor having the same value asthe resistors connected between said validation circuits and the inputterminals of said operational amplifier.
 6. A phase meter as defined inclaim 1 wherein each validation circuit includes first, second, andthird AND gates each having a pair of inputs, the outputs of said firstand second AND gates being connected to the respective inputs of saidthird AND gate whose output is connected to an input of said second ANDgate, the other input of said second AND gate and an input of said firstAND gate being connected together to form one input of said validationcircuit and the other input of said first AND gate forming the otherinput of said validation circuit.
 7. A phase meter as defined in claim 1wherein the output of each validation circuit is connected to an inputof said operational amplifier through a respective resistor, all of theresistors connected to the inputs of said operational amplifier havingan equal value.